Aspen Leaf Quality Mfects Gypsy Moth (Lepidoptera: Lymantriidae) Susceptibility to Bacillus thuringiensis

We assessed variation in Bacillus thuringiensis subsp. kurstaki toxicityagainst gypsy moth, Lymantria dispar (L.), larvae reared on different aspen trees, and how such variation maybe linked to foliar chemistry, particularly phenolic glycosides. Larvae were reared on foliage from Five different trees. LD50 were determined using third instars and six doses of B. thuringiensis (Foray 48B). Results showed 100-foldvariation in B. thuringiensis toxicity for larvae reared on different trees. Chemical analyses of leaf material suggested that condensed tannins and perhaps phenolic glycosides affect B. thuringiensis toxicity. Feeding studies with artificial diets containing various levels of B. thuringiensis and phenolic glycosides confirmed that the secondary compounds can strongly enhance the efficacy of B. thuringiensis.